This invention relates to a device for supporting a workpiece to be machined.
Unexamined Japanese Patent Publication 2-269513 discloses a method of clamping a workpiece to be machined, in which the clamping jaws are opened by feeding compressed air into a passage or branched passages through an outer sheath of an air tube or through the air tube, and the jaws are closed to clamp the workpiece by stopping the supply of compressed air or by reducing its pressure after fitting an inner recessed part of the workpiece onto a stopper (outer clamping method).
In another method, an inner protrusion of the workpiece is brought into abutment with the stopper and the clamping jaws engage the workpiece within a recess defined therein. Then by feeding compressed air into the passage or branched passages, the clamping jaws are opened, thus clamping the workpiece (inner clamping method).
The outer clamping method, in which the workpiece is clamped using the restoring force of the diaphragm, has a problem in that the clamping jaws tend to shift outward due to the centrifugal force produced while in rotation in proportion to the mass of the clamping jaws. This reduces the clamping force. Thus, when using this method it was difficult to increase the revolving speed of the workpiece while maintaining safety.
Further, since the outer clamping force of the clamping jaws cannot be reduced below a certain level due to the fact that they are controlled by the restoring force of the diaphragm, the workpiece may be deformed if it is to thin. Thus, it was impossible to machine thin workpieces.
With the inner clamping method, after the clamping jaws are opened and pressed against the inner surface of the workpiece by feeding compressed air to the device, a centrifugal force is produced in proportion to the mass of the clamping jaws while in rotation. Thus, the clamping jaws are pressed more strongly against the workpiece. Thus, the workpiece is pushed outward and may be deformed. It was thus impossible to machine a thin workpiece.
Further, in case of the inner clamping method, if the air compressor or the air tube should be broken, the clamping force will be relieved and an accident may result.